This invention relates generally to well blowout preventers, and more particularly concerns packer units and inserts used in such equipment.
U.S. Pat. No. 2,609,836 to Knox describes annular type blowout preventer packing units which incorporate like metal inserts spaced about the packer central axis, and embedded by an elastomeric, such as rubber, body. Upon inward constriction of the unit about a well drill pipe, or upon itself, the rubber is squeezed radially inwardly with resistance imposed by the inserts to which the rubber is anchored. Well pressure exerted upwardly upon the stretched or extended rubber also tends to displace it upwardly, so that the material is subjected to strain both radially and vertically. This causes fatigue and weakening of the material, particularly after repeated closure of the preventer unit, so that each unit is normally rated as to its capability to safely sustain or withstand a certain number of closures. Efforts have been made to increase this number of closures, but the problem of extreme stretching of the rubber has limited the success of such efforts.